我想使用表上的distontOn进行通用的平滑查询，以计算列中的不同元素。
def countDistinct(table: TableQuery[_], column: Rep[_]): DBIO[Int] =
table.distinctOn(_ => column).length.result
上面的代码由于以下原因而无法编译：
No matching Shape found.
[error] Slick does not know how to map the given types.
[error] Possible causes: T in Table[T] does not match your * projection,
[error] you use an unsupported type in a Query (e.g. scala List),
[error] or you forgot to import a driver api into scope.
[error] Required level: slick.lifted.FlatShapeLevel
[error] Source type: slick.lifted.Rep[_]
[error] Unpacked type: T
[error] Packed type: Any
[error] table.distinctOn(_ => column).length.result
FlatShapeLevel而不是Rep[_]也不起作用。我正在使用光滑3。